Search PubMed⌕ Search

Biomedical subjects

D M Mirvis

Publications and source records attributed to D M Mirvis.

144 records · Page 8Linked to original sources
PubMed1977

Symptomatic swallowing-induced paroxysmal supraventricular tachycardia.

A 55 year old woman with palpitations during ingestion of food or drink was evaluated with surface, esophageal and dynamic electrocardiographic techniques. Recordings documented the consistent induction of supraventricular tachycardia by swallowing; no definable gastrointestinal or other cardiac abnormality was present. Nine previously reported cases are reviewed, with special reference to the role of vagovagal reflexes in the pathogenesis of this unusual clinical syndrome.

Deglutition↗
PubMed1977

The electrocardiographic image surface revisited.

An image torso may be viewed as a one-to-one transform of a physical volume conductor to a geometric form which defines both the axis and sensitivity of any electrocardiographic connection. In this report, the image surfaces of laminar, spherical, rectangular and humanoid physical torsos are explored theoretically and experimentally. All proved to be rounded or spherical in form despite the marked differences in the configuration of the physical conductor. Moderate degrees of dipole eccentricity induced only small departures from this basic circular pattern. Introduction of phase inhomogeneity, however, resulted in more striking deviations from roundness.

Animals↗
PubMed1977

Left precordial isopotential mapping during supine exercise.

Junctional depression is often observed during physical exercise in overtly normal subjects. To explore its pathogenesis, 15 normal volunteers were studied during supine, bicycle ergometer, submaximal stress tests. Electrocardiograms were simultaneously recorded from 42 electrodes on the left anterior precordium at two minute intervals at rest and during exercise. Data were used to construct isopotential maps throughout the P-QRS-T intervals. At rest, maps throughout the ST segment were dominated by a single maximum along the upper left sternal border. During exercise, all subjects developed junctional depression that was maximal along the lower left sternal border. Exercise maps during the early to mid-ST segment showed an intense minimum along the lower left sternal border that was continuous with terminal QRS forces in both intensity and location. Later in ST, this minimum decreased in strength and was replaced by a maximum located in the same area as that observed at rest. These observations suggest that junctional depression is the result of competition between two effects, one being normal repolarization which is obscured in the early ST segment by the second, possibly representing delayed terminal depolarization forces.

Action Potentials↗
PubMed1977

Relative dipolar behavior of the equivalent T wave generator: quantitative comparison with ventricular excitation in the rabbit heart.

We studied the relative dipolar and nondipolar content of signal energy throughout ventricular excitation and recovery in 34 isolated, perfused rabbit hearts, suspended in an electrolyte-filled spherical chamber. Computer-processed signals were derived from 20 evenly spaced tank-surface electrodes, and a single, moving, equivalent cardiac dipole generator was optimally fitted to the recorded potentials for each 1-msec sampling interval. Superimposed, time-based plots of signal energy for the 34 preparations showed ventricular excitation to be strikingly more nondipolar than was recovery. In terms of the summed square ratio of nondipolar residual energies, overall nondipolarity of QRS exceed that of ST-T by 41%. Furthermore, the maximum instantaneous ratio during QRS was considerably greater than during the ST-T. Evaluation of paired differences, comparing nondipolar behavior throughout QRS with all of ST-T, proved highly significant (P less than .005). We also found that in contrast to the considerable mobility exhibited by the equivalent QRS dipole, the ST-T dipole locus remained nearly stationary during most of ventricular recovery. Presumably because repolarization is temporally and spatially a relatively diffuse process, it may generate electrical fields which are notably more dipolar than those caused by depolarization.

Animals↗
PubMed1977

Detection and localization of multiple epicardial electrical generators by a two-dipole ranging technique.

The ability of a numerical procedure to detect and to localize two experimentally induced, epicardial dipolar generators was tested in 24 isolated, perfused rabbit heart preparations, suspended in an electrolyte-filled spherical tank. Electrocardiograms were recorded from 32 electrodes on the surface of the test chamber before and after placement of each of two epicardial burns. The second lesion was located either 180 degrees, 90 degrees, or 45 degrees from the first. Signals were processed by iterative routines that computed the location of one or two independent dipoles that best reconstruced the observed surface potentials. The computed single dipole acounting for 99.68% of root mean sequare (RMS) surface potential recorded after the first burn was located 0.26 +/- 0.10 cm from the centroid of the lesion. Potentials recorded after the second lesions were fit with two dipoles that accounted for 99.36 +/- 1.51% of RMS surface potentials and that were located 0.42 +/- 0.26 cm and 0.57 +/- 0.49 cm from the centers of the corresponding burn. Seventy-one percent of computed dipoles were located within the visible perimeter of the burn. Thus, two simultaneously active dipolar sources can be detected and accurately localized by rigorous study of the generated electrical field.

Animals↗
PubMed1977

Rate-dependent variation in the duration of the QRS complex with left anterior fascicular block.

The case of a 67-year-old man with combined ischemic and valvular heart disease is presented. Electrocardiographic abnormalities included left anterior fascicular block with a variable duration of the QRS complex. The width of the QRS complex was dependent on the length of the cycle, being broader with short than with long preceding R-R intervals. This is interpreted as a tachycardia-dependent focal block coexisting with a fixed delay in fascicular conduction.

Aged↗
PubMed1976

Wenckebach-type exit block from an ectopic focus as a cause of variable coupling.

Intermittent bigeminal and trigeminal ventricular premature beats were recorded in an otherwise healthy 14 year old male. Coupling intervals progressively lengthened until an ectopic beat was dropped. Odd numbers of sinus beats occurred between bigeminal runs. This rhythm is interpreted as being due to Wenckebach-type block in an exit pathway from the ectopic focus, resulting in concealment of the persistently active extrasystolic mechanism.

Adolescent↗
PubMedDate not supplied

Effects of coronary occlusion on transmural distribution of blood flow in the interventricular septum and left ventricular free wall.

Collateral flow to the interventricular septum in the dog was measured after septal artery ligation (N = 8) and compared to that in the left ventricular free wall after occlusion of the left anterior descending coronary artery (N = 10) in other animals. Flow was quantitated by radiolabelled microsphere injection before, and 90 s, 2 h and 4 h after occlusion. Perfusion territory size was measured after colored dye infusion; the septal artery bed occupied 21.74 +/- 5.44% of the left ventricle and was significantly smaller than the anterior descending artery zone (40.72 +/- 7.56%). Regional blood flow prior to occlusion was equal in both beds and symmetric across the ventricular wall; endocardial/epicardial and left/right ratios in the anterior descending and septal artery beds were 0.97 +/- 0.14 and 1.14 +/- 0.17, respectively. 90 s after occlusion, left and right septal and endocardial and epicardial anterior descending flows were significantly (p less than 0.05) reduced. Right septal flows exceeded left sided flows to produce a transseptal gradient. However, right septal flow was significantly greater than epicardial anterior bed values, and free wall endocardial/epicardial was significantly lower than septal left/right ratios. By 2 h after occlusion, left and right septal flows were no longer significantly different from preocclusion values, whereas anterior descending flows remained significantly below control for the full 4-h period. Thus, significant differences between the two beds exist, with greater acute collateral flows and more rapid correction of flow deficits in the septum than in the free wall.

Animals↗
PubMedDate not supplied

Myocardial infarction following acute occlusion and reperfusion of the septal coronary artery.

It has been demonstrated that temporary occlusion of major epicardial arteries of the dogs produces a nontransmural myocardial infarction (MI) whose size is reduced by early reperfusion. This study was undertaken to determine the location and extent of MI following acute occlusion and reperfusion of the septal artery (SA). The SA was occluded for four hours in group I (7 dogs). Occlusion time for group II (6 dogs) was 2 hours and for group III (6 dogs) was 1 hour, followed by 2 and 3 hours of reperfusion, respectively. The hearts were then removed and cut into transverse slices from base to apex. The triphenyl tetrazolium chloride technique identified the areas of infarction, which were quantitated with a microcomputer-based graphics system. To determine the extent of necrosis across the interventricular septum (IVS), the IVS was divided into 5 transverse segments of equal depth and the amount of MI was determined for each. In group I, MI involved 3.42 +/- 0.9% (mean +/- SEM) of the left ventricle (LV) and 13.49 +/- 3.4% of the IVS. In group II, 6.11 +/- 1.3% of the LV and 25.00 +/- 5.5% of the IVS were infarcted. In group III, 5.63 +/- 1.3% of the LV and 31.9 +/- 14.3% of the septum were infarcted. MI was larger on the left side of the IVS than on the right in all groups, and the extent of MI did not differ significantly between the three groups. This study showed that early reperfusion of the SA did not reduce MI as reported for other coronary beds.

Animals↗
PubMedDate not supplied

The pulmonic valve echogram in the assessment of pulmonary hypertension in children.

Echocardiographic patterns of pulmonary valve motion and right-sided systolic time intervals were correlated with pulmonary arterial hemodynamics in 56 children with congenital heart defects. The sensitivity of an abnormal a-dip, reduced e-f slope or mid-systolic valve closure in detecting elevated pulmonary artery diastolic or mean pressures or pulmonary to systemic resistance ratio varied from 36 to 62%. Specificities ranged from 50% (e-f slope for increased Rp:Rs) to 93% (mid-systolic closure for PA diastolic pressure greater than 10 mm Hg). Systolic-time-intervals (RPEP/RVET) did not significantly correlate with pulmonary hemodynamics. We therefore conclude that these echocardiographic features are insufficiently sensitive to be clinically applied to detect pulmonary hypertension in pediatric patients, and that only 2 (a-dip and mid-systolic closure) were of sufficient specificity to be useful.

Adolescent↗
PubMedDate not supplied

Myocardial disease in Rocky Mountain spotted fever: clinical, functional, and pathologic findings.

Rocky Mountain spotted fever is an acute febrile illness with a significant mortality rate. Cardiac involvement has been sporadically reported, but is more common than appreciated from pathologic studies. The lesion is one of vasculitis, with secondary thrombosis and tissue necrosis. Cardiac function abnormalities may be detected by echocardiography and may persist after resolution of other manifestations of disease. Myocardial involvement is frequently present in Rocky Mountain spotted fever; close monitoring and an aggressive therapeutic approach are essential if the high case fatality rate (7%-11%) is to be reduced. Pathophysiologic consequences of damage to other organ systems may affect circulatory function and should be carefully evaluated.

Adolescent↗
PubMedDate not supplied

Hemodynamic response to profound hypoxia in intact rhesus monkeys.

Respiring rhesus monkeys with 2.5 or 4.5% oxygen greatly decreased their cardiac contractility, stroke volume and blood pressure but altered their total peripheral vascular resistance only slightly and inconsistently. All monkeys exposed to 15 minutes and 2 of 4 exposed to 30 minutes of hypoxia recovered and survived without brain injury. Though all animals recovered full cardiovascular function immediately after they were reoxygenated, 2 respired with 4.5% oxygen for 30 minutes began showing declines in blood pressure after a delay of 1 to 2 hours and both subsequently died in shock. Their reductions in blood pressure were associated with reductions in cardiac contractility and stroke volume. The hypotension the animals exhibited both during hypoxia and during development of shock afterwards resulted from pump failure rather than a reduced vascular resistance or an inadequate venous return.

Animals↗
PubMedDate not supplied

Trends in burnout and related measures of organizational stress among leaders of Department of Veterans Affairs medical centers.

Psychological burnout significantly and detrimentally affects individuals and the organizations for which they work. Leaders with burnout often display characteristics that are the opposite of those required to implement major organizational change. This study was undertaken to assess the level of psychological burnout of leaders of the Department of Veterans Affairs (VA) medical centers during a period of rapid change. The objective was to quantify trends in the level of burnout and associated measures of psychological stress. Surveys of medical center directors, associate medical center directors, and chiefs of staff of each VA medical center were conducted in 1989, 1992, and 1997 to evaluate burnout, role characteristics, and job satisfaction. Burnout was measured using the Maslach Burnout Inventory and scored using the phase model of burnout. Findings demonstrated higher prevalences of more advanced levels of burnout in the 1992 and 1997 surveys than in the 1989 survey. Role clarity, perceived adequacy of resources to complete assigned tasks, and several measures of job satisfaction were lower in the 1997 survey compared to the earlier survey data. Therefore, psychological burnout and other indicators of stress increased during the 1989 to 1997 study period. These findings suggest cause for concern as the largest integrated healthcare system in the United States undertakes major organizational change to meet present and future challenges.

Burnout, Professional↗